EVSE using Relay over Contactor - would a contactor give a longer lifetime?

Thread Starter

flivor

Joined Mar 11, 2023
2
Hello,

While relays have a size advantage, an electrical engineer from a partner team tells me we should use contactors instead of relays for our ~7kW (single phase) and 22kW (3 phase) charge points. He said that the relays, when operating for long periods will have a higher chance of failing. While I am inclined to believe him, I am wondering if over the lifetime of a charger (let's say we expect it to last at least 7 years), all else considered equal, will there (likely) be any noticeable increase in rate of failure of the relay vs contactor? I'm not sure if he's being fastidious or is right to make this comment - I've noticed many AC EVSE / charge point manufacturers are using relays over contactors.

Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
28,772
I would agree that using contactors sounds more suitable once you get up into the loads you are quoting, 7Kw - 22Kw.
Relays tend to fall into the category of up to 15amps, maybe 30A tops.
Once this is exceeded, contactors sound the most suitable.
 

MisterBill2

Joined Jan 23, 2018
19,033
The two categories seem to overlap a bit, and more importantly, there are wide spreads of quality in both. So the choice will depend on the sort of application: is this a commercial application where the chargers will be produced in large productio runs and sold all over? Or is it an application for use within an organization? Or neither of these? In some applications the correct contactor would be the preferred choice, but you need to be certain that it is built for constant activation because a battery charger will be charging for hours at a time.
Thus the primary consideration will be the specifications and lifetime rather than initial cost,
 

MaxHeadRoom

Joined Jul 18, 2013
28,772
The two categories seem to overlap a bit, and more importantly,
So where does the distinction start and end? when does a relay become a contactor??
How is it determined??
There are special categories for many of each, e.g. Magnetic arc blow-out, Special Purpose, Safety Relay (force guided contacts), the list goes on.
It could be said, a Contactor IS a relay! :rolleyes:
 

MaxHeadRoom

Joined Jul 18, 2013
28,772
....................And a Convoluted answer from Google. :rolleyes:


"What is the difference between a contactor and a relay?"



Image result for contactor definition


"Relays are used to control contacts of an electrical circuit due to a change of parameters or conditions in the same circuit or any other associated circuit.
Contactors, on the other hand, are used to interrupt or establish connections in an electrical circuit repeatedly under different conditions."
 

Ian0

Joined Aug 7, 2020
10,054
If using a relay, make sure that the contacts are rated at 400V, and make sure that it can make or break the full capacity.
An advantage of (most) contactors is that the contact separation when the contacts are open is large enough to consider the load "isolated" for safety purposes.
 

Thread Starter

flivor

Joined Mar 11, 2023
2
Thanks for your comments everyone. I still am wondering why so many chargepoint manufacturers go for the on-PCB relay though? Is it just size? Convenience of being onboard the PCB?

@Ian0 would you feel 'safe' using through-hole (PCB mounted) 400V rated relays that were supplying 32A+ to cars for >16 hours a day for half a decade?
 

Janis59

Joined Aug 21, 2017
1,855
Even contactor are different from contactor. Remember that three-liter sized old russian contactors? But they served at max current hundred years until the spiders made the shortcome. And then the Polish and Chineese contacors came into market - cheap, small, nice. BUT! I spoke with main engineer of company producing the air compressors. They ended the russian 16A contactors in stock and bought in the Polish 16A. Motor 220V 2.2kW (10A). After new compressors flooded the market, after 3 month term the 80% was returned to warranty. All have burned out that relay. They bought up the 25A Polish. The same result. They bought up the Chineese 35A. Result the same. Now they are buying an American what are some 10x expensiver, but at least their compressors are stable. So... yes, of course the 5x3 mm silver pad in contactor is more trustable than d=1 mm silver ball in relay. But everything depends on the trust to producer is not lying.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
19,033
There is no adequate substitute for using enough of the correct materials in a power handling product. Those cheap versions are evidently based on the assumption that users will not actually require operating at the claimed ratings.
 

MaxHeadRoom

Joined Jul 18, 2013
28,772
Since the Advent of DIN style contactors, I have stuck with Telemecanique, (now Schneider). most have been in service for a few decades now and still going.
They also offer quite a few add on options to the basic contactor.

1678721973813.png
 

MaxHeadRoom

Joined Jul 18, 2013
28,772
Thanks for your comments everyone. I still am wondering why so many chargepoint manufacturers go for the on-PCB relay though? Is it just size? Convenience of being onboard the PCB?
They are also used extensively in different kinds of appliance's and are a common cause of failure, especially at the solder joints on the board, another is that the vent hole is not being opened after board completion and de-fluxing etc, this causes premature failure due to the air ionization in the sealed relay.
Primary reason for using, Cost!
 

MisterBill2

Joined Jan 23, 2018
19,033
Especially in vehicle charging systems accessible to the general public it seems that quality, which I equate to longer functional life, is not a major requirement. Thus in the harsh reality of use, the products fail. Part of this is due to the inclusion of features by those who have no grasp of what quality is.
 
Top